Tkinter中temperatureA无法从下拉框取值的技术问题

代码中第56行的temperatureA = watertemperature.get()无法从watertemperature下拉菜单获取选中值，但手动赋值（比如temperatureA = "40"）时后续代码能正常运行，请问原因是什么？

相关代码：

import tkinter
from tkinter import messagebox, ttk
from tkinter import ttk  # set root root = tkinter.Tk()

root = tkinter.Tk()
root.geometry("270x150")

a = tkinter.Label(root, text="Technology")
a.grid(row=1, column=1, columnspan=2, padx=10, pady=2,
       sticky='w')  
# grid 
X1 = ["18.3", "4.7", "15.9", "5.5", "50"] 
X2 = ["74", "5.8", "21.1", "6.56", "50"] 
X3 = ["28.7", "7.5", "29.3", "8.5", "50"] 
X4 = ["41", "9.4", "23", "10.3", "40"] 
X5 = ["44.7", "11.8", "45.2", "13.4", "50"] 
X6 = ["78", "11.8", "48.7", "11.9", "35"]

units = [X1 + X2 + X3 + X4 + X5 + X6]

type = ["Heat Pumps", "Heat Interface Units", "District Heat Networks", "photovotaic panels"]

watertemp = [["35", "40", "45", "50", "55", "60", "65"],  ["44", "22", "14", "75"],  ["12", "28", "15"],  ["25",
                                                                                                                   "42",
                                                                                                                   "91"]] 
 
techtype = ttk.Combobox(root, width=37, value=(type))
techtype.grid(row=3, column=1, columnspan=2, padx=10, pady=2, sticky='w')


def callback(eventObject):
    abc = eventObject.widget.get()


    water = techtype.get()
    index = type.index(water)
    watertemperature.config(values=watertemp[index])
    temperatureA = watertemperature.get()
    print(temperatureA)
      # Find value from index location
    temperature = [item[4] for item in units]


    # Find value index
    degreesindex = [i for i in range(len(temperature)) if temperature[i] == temperatureA]

    # Creates list from temperature
    res_list = [units[i] for i in degreesindex]

    # Find the heating load
    duty = [item[0] for item in res_list]

    print(duty)

watertemperature = ttk.Combobox(root, width=37, value=watertemp)
watertemperature.grid(row=4, column=1, columnspan=2, padx=10, pady=2, sticky='w')
watertemperature.bind('<Button-1>', callback)

root.mainloop()

问题原因 #

1. 绑定事件时机错误：给watertemperature绑定了<Button-1>（左键点击）事件，这个事件在用户刚点击下拉框、还没选择任何选项时就触发，此时下拉框没有选中值，自然拿不到内容。
2. 逻辑顺序混乱：在callback里刚更新完watertemperature的选项列表，立刻调用get()，但用户还没来得及选择新选项，获取的要么是空值，要么是旧值。
3. 初始化参数错误：watertemperature初始化时value=watertemp，但watertemp是二维列表，不符合Combobox的value参数要求（需为一维列表），导致初始状态下拉框没有正确选项。

解决方案 #

1. 调整事件绑定 #

把watertemperature的绑定事件改成<<ComboboxSelected>>，这个事件仅在用户选中下拉框选项后触发，能确保拿到有效选中值。同时给techtype绑定该事件，用来更新watertemperature的选项列表。

2. 拆分逻辑 #

把“更新水温选项”和“计算负载”的逻辑分开：

• 用户选择技术类型时，仅更新watertemperature的可选值；
• 用户选择水温后，再执行后续计算逻辑。

3. 修正初始化 #

watertemperature初始时设置value=watertemp[0]（默认显示第一个技术类型的水温选项），或者先设为空，等用户选技术类型再更新。

修改后的代码 #

import tkinter
from tkinter import ttk

root = tkinter.Tk()
root.geometry("270x150")

a = tkinter.Label(root, text="Technology")
a.grid(row=1, column=1, columnspan=2, padx=10, pady=2, sticky='w')  

X1 = ["18.3", "4.7", "15.9", "5.5", "50"] 
X2 = ["74", "5.8", "21.1", "6.56", "50"] 
X3 = ["28.7", "7.5", "29.3", "8.5", "50"] 
X4 = ["41", "9.4", "23", "10.3", "40"] 
X5 = ["44.7", "11.8", "45.2", "13.4", "50"] 
X6 = ["78", "11.8", "48.7", "11.9", "35"]

# 修正：每个X列表作为单独元素，避免后续索引错误
units = [X1, X2, X3, X4, X5, X6]  
# 避免使用Python内置关键字type，修正拼写错误
tech_types = ["Heat Pumps", "Heat Interface Units", "District Heat Networks", "photovoltaic panels"]  

watertemp_options = [
    ["35", "40", "45", "50", "55", "60", "65"],
    ["44", "22", "14", "75"],
    ["12", "28", "15"],
    ["25", "42", "91"]
] 

# 技术类型下拉框
techtype = ttk.Combobox(root, width=37, value=tech_types)
techtype.grid(row=3, column=1, columnspan=2, padx=10, pady=2, sticky='w')

# 水温下拉框：初始显示第一个技术类型的水温选项
watertemperature = ttk.Combobox(root, width=37, value=watertemp_options[0])  
watertemperature.grid(row=4, column=1, columnspan=2, padx=10, pady=2, sticky='w')

def update_watertemp_options(event):
    # 选择技术类型时更新水温选项
    selected_tech = techtype.get()
    if selected_tech in tech_types:
        index = tech_types.index(selected_tech)
        watertemperature.config(values=watertemp_options[index])
        watertemperature.set('')  # 清空之前的选择

def calculate_load(event):
    # 选择水温后执行计算逻辑
    temperatureA = watertemperature.get()
    if not temperatureA:
        return  # 未选水温直接返回
    
    print(f"选中的水温：{temperatureA}")
    # 提取每个units元素的第4个值（索引4）
    temperature_list = [item[4] for item in units]
    
    # 找到匹配的索引
    degreesindex = [i for i, temp in enumerate(temperature_list) if temp == temperatureA]
    
    # 筛选对应的units元素
    res_list = [units[i] for i in degreesindex]
    
    # 提取加热负载
    duty = [item[0] for item in res_list]
    
    print(f"计算得到的负载：{duty}")

# 绑定正确的事件
techtype.bind('<<ComboboxSelected>>', update_watertemp_options)
watertemperature.bind('<<ComboboxSelected>>', calculate_load)

root.mainloop()

内容的提问来源于stack exchange，提问作者James Knight